1. Field of the Invention
The present invention relates to an analog system for automatic mill slowdown control.
2. Description of the Prior Art
In the operation of a rolling mill, as for example, a non-reversing tandem cold steel strip reduction mill, typically a strip of material is unwound from a payoff reel, threaded through the roll stands, and wound on a windup reel. When the threading operation is completed, the mill is accelerated from thread speed to a preselected run speed, and run at this speed until a point where mill deceleration is initiated to provide a safe tailoff, i.e. insure that the trailing end will not go through the mill at an excessive speed so as to endanger personnel as well as property. (Usually the tailoff speed is set equal to the thread speed.)
Similar operating conditions obtain in reversing type cold steel rolling mills as well as reversing rolling mills for materials other than cold steel strip. In the reversing type mill, a single roll stand is usually employed, and the start up procedure, run and slowdown sequence just described, is effected for each pass in the mill operation.
Obviously, in order to maximize productivity, it is desirable to run the mill at the highest possible speed and initiate slowdown at the latest point in time consonant with safety. If slowdown is begun too early, a wasteful amount of material will be processed at slow or thread speed. Optimum slowdown depends principally upon the operating run speed of the mill, and upon the number of strip wraps required on its payoff reel to enable mill deceleration to tailoff speed just as the strip tail end is coming off the payoff reel and entering the mill.
In those installations where a programmed digital computer is used for mill control a highly accurate selection and detection can be had of the slowdown payoff coil diameter for the purpose of optimizing the initiation of the slowdown signal. However, the utilization of a computer is not always economically feasible, so resort must be had to less expensive analog solutions.
One automatic slowdown control is described in U.S. Pat. No. 3,518,857 to C. O. Hancock et al for "Rolling Mill Automatic Slowdown Control." In this latter patent, the speeds of a payoff reel and an entry deflector roll respectively are compared. When the two speeds reach a predetermined relationship, mill slowdown is initiated. Control is adjustable as a function of strip gauge and mill speed to allow earlier mill slowdown for heavier gauge and/or faster mill run speed.